The invention relates to selectable-yield munitions and more specifically to spiral linear shaped charge jets.
Explosive ordnance is defined as any component or assembly that contains or is operated by explosive materials. The ability to rapidly release directed energy to perform multiple operations nearly simultaneously is the major attribute of explosive ordnance. To be useful in the aerospace industries and other industries, explosive components' output must be controlled. Selectable-yield munitions have been identified by United States Department of Defense planners as a means to reduce collateral damage while optimizing lethality against a broad target set. Explosively actuated devices are generally lighter and smaller than equivalent mechanical or electromechanical devices, which makes them attractive for space applications. Typical tasks include launch vehicle hold-down release, engine ignition, stage separation, fairing separation, and appendage deployment. In the military sector, multiple inventory weapons—ranging from concrete-filled bombs to 250-lb, 500-lb, 1000-lb, and 2000-lb general purpose bombs—could be replaced by a single selectable-yield munition.
One method of controlling, or selecting, the yield of munitions that has received a great deal of attention is the use of shaped charge jets (SCJ's) to deflagrate (burn) a portion of the main charge explosive to reduce the overall yield prior to a the main charge being detonated. This is accomplished by detonating the explosive within the shaped charge jet, which causes the shaped charge jet liner to form a high velocity jet. The jet formed from the liner penetrates the main charge explosive. The high pressure, temperature, and friction induced on the main charge from the jet causes the main charge explosive to burn. The reaction induced by the shaped charge jet must be kept below the minimum pressure and temperature reaction threshold, specific to the explosive being used in the main charge, which would lead to detonation of the main charge through a shock to detonation or deflagration to detonation reaction. Current state-of-the-art shaped charge jet fabrication techniques and knowledge of explosive initiation properties has enabled shaped charge jets to be optimized to great extent for deflagrating explosives without causing a transition to detonation.
The rate at which the mass of the explosive is reduced by the deflagration reaction is highly dependent on the initial surface area affected by the jet. For a conical shaped charge jet, the initial reacted area is mostly limited to the single axis path of the jet, i.e., similar to path of a bullet through the charge. For linear shaped charge jet, the initial reacted area is limited to the cross-sectional plane of which the jet cuts through the explosive, i.e., similar to a knife blade cutting through the charge. In both cases the volume affected by a single shaped charge jet is very limited, and the reaction time is unsuitable for most military applications where a dial-a-yield capability would be useful. For example, a free fall general purpose bomb traveling at 1000 feet per second will move 1 foot per millisecond. Therefore, control of the yield would need to be within a few milliseconds to effectively attack a target once the target detection device trigger threshold is met for weapon initiation. This is well beyond the deflagration rate attainable with a single conical or linear shaped charge jet. Therefore, a large number of conical or linear shaped charge jets using current state-of-the-art design techniques would be required to precisely control the yield of a large explosive volume, i.e., net explosive weight, weapon over the potential range of outputs from high-order detonation to full low-yield deflagration on a time scale that is suitable for many military target engagements.